Its actually a really complex task that can be very controversial and steeped in politics. The process affects almost every interest group that you can imagine. Because the stakes are so high, the process is often undertaken under a microscope and litigation usually follows the completed redistricting process. You can keep track of all the twists and turns state by state with our Redistricting Almanac.

Redistricting is done to ensure the principle of “one person, one vote”: that voting power and representation in our legislative chambers is distributed equally, based on population. Before a series of court cases in the 1960s, legislative districts weren’t required to be redrawn based on population, and in many states, districts had remained unchanged for decades. That led to legislators or Congressmembers representing widely varying numbers of people. It wasn’t fair, said the courts, to have districts of widely divergent population size—some with 10 times as many residents as others—all represented by a single legislator. Since then it is settled law that every 10 years, after the census data is released, states are required to redraw the lines. (That doesn’t preclude redistricting more frequently depending on your state's laws, but that is less common.) (NCSL.org) Read More

Generally, the task of redistricting falls on state legislatures. Even in states where a commission has been handed the responsibility for redistricting, the process generally still includes some role for the legislature in most states, often (but not always) the right to appoint members. The process remains much the same, whether it is conducted by the legislature or by a commission. Commissions need similar technical and financial support, even before their members are appointed. (NCSL.org)  Read More

Congress has generally left redistricting rules to the states and courts have stepped in to fill the vacuum, especially when it comes to equal population requirements, the prohibition on racial gerrymandering, and compliance with the Voting Rights Act of 1965. Despite court intervention, a large part of redistricting consists of best practices that have evolved over the decades; they are more widely known as “traditional redistricting principles.”

These principles are now recognized by courts as general practice standards that have evolved over time, and while they are not necessarily legal requirements, (although many states have codified some of these principles), courts often consider the level of adherence to these principles evidence of other constitutional violations.  Read More

See CRS Report https://crsreports.congress.gov/product/pdf/IN/IN11618

Deadlines for Adoption

Many states have specific deadlines for enacting redistricting maps. Many of those deadlines fall in the 2^nd year after the census. If there is no specified deadline in state law, any voter in a state will have standing to sue in court with a claim that the current district map is malapportioned, or in violation of the equal population requirement. Deadlines notwithstanding, most courts would side with the plaintiff if the legislature or other redistricting authority has not enacted a map before elections in the second year after the census.

Voting Rules and Other Procedures

Redistricting maps may require supermajorities for adoption by the legislature and commissions may have rules requiring members from both parties to be in favor of a map.  In Colorado, to enact a map, the redistricting commission must approve it with a two-thirds majority and at least two commissioners that are unaffiliated with either major party must vote for adoption.  Read More.

Gerrymandering is the manipulation of political district boundaries to benefit an identifiable group such as a racial or ethnic group or political party. Gerrymandering as a general matter is not illegal, however if the manipulation violates constitutional rights or other rules or statutes, a court can invalidate individual districts or entire maps.
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There are two types of legally recognized causes of action for gerrymandering; racial gerrymandering and partisan gerrymandering. The legal history and requirements for the two differ significantly.

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More on partisan gerrymandering

More on racial gerrymandering

The federal legal framework addressing race in redistricting has evolved considerably since the sixties. The Voting Rights Act of 1965 and Supreme Court precedent make up the bulk of the rules on race in redistricting. The court and certain provisions of the VRA work to balance the tension between political goals in redistricting and protecting the representational rights of minorities. The court has worked to protect not only minority voters but voters of every race from the diminution of their representational rights. Specific legal rules, however, do address intentional and unintentional minority vote dilution.  Read More

Census Redistricting Data

Title 13 of the U.S. Code in Public Law 94-171 requires the Census Bureau to distribute specified census data to governors, legislative bodies or other officials responsible for redistricting, by Spring in the year following the census. While most states use this decennial census data for redistricting, 21 states require use of this data in statute.

It is important to note that the decennial census data includes more than the demographic profile of the country’s population. It also includes specific detailed geographic information on nearly every geographic feature imaginable, including streets, water features, political boundaries, election precincts, prisons, and many other land features.  Read More

The U.S. Census counts prisoners as residents of the prison they are located in. Prisoner reallocation is the process of adjusting the census data used in redistricting so that prisoners are counted at their previous home address as opposed to the prison. While not a requirement, some states have elected to reallocate prisoners before redrawing maps as prison populations are quickly becoming a representational issue for voters.  Read More